The present invention relates to a compact optical device and, more particularly, to a compact optical device which can be used in personal hand-held devices, such as personal digital assistant (PDA), portable telephones and the like.
Miniaturization of electronic devices has always been a continuing objective in the field of electronics. Electronic devices are often equipped with some form of display, which is visible to a user. As these devices reduce in size, there is an increase need for manufacturing compact displays, which are compatible with small size electronic devices. Besides having small dimensions, such displays should not sacrifice image quality, and be available at low cost. By definition the above characteristics are conflicting and many attempts have been made to provide some balanced solution.
An electronic display may provide a real image, the size of which is determined by the physical size of the display device, or a virtual image, the size of which may extend the dimensions of the display device.
A real image is defined as an image, projected on a viewing surface positioned at the location of the image, and observed by an unaided human eye. Examples of real image displays include a cathode ray tube (CRT) or a liquid crystal display (LCD). Typically, desktop computer systems and workplace computing equipment utilize CRT display screens to display images for a user. The CRT displays are heavy, bulky, and not easily miniaturized. For a laptop, a notebook, or a palm computer, flat-panel display is typically used. The flat-panel display may use LCD technology implemented as passive matrix or active matrix panel. The passive matrix LCD panel consists of a grid of horizontal and vertical wires. Each intersection of the grid constitutes a single pixel, and is controlled by a LCD element. The LCD element either allows light through or blocks the light. The active matrix panel uses a transistor to control each pixel, and is more expensive.
The flat-panels are also used for miniature image display systems because of their compactness and energy efficiency compared to the CRT displays. Various configurations of miniature display systems using flat-panel display and reflective lighting technique can be found in U.S. Pat. No. 5,808,800.
Small size real image displays have a relatively small surface area on which to present a real image, thus have limited capability for providing sufficient information to the user. In other words, because of the limited resolution of the human eye, the amount of details resolved from a small size real image may be insufficient.
By contrast to a real image, a virtual image is defined as an image, which cannot be projected onto a viewing surface, since no light ray connects the image and an observer. A virtual image can only be seen through an optic element, for example a typical virtual image can be obtained from an object placed in front of a converging lens, between the lens and its focal point. Light rays, which are reflected from an individual point on the object, diverge when passing through the lens, thus no two rays share two endpoints. An observer, viewing from the other side of the lens would perceive an image, which is located behind the object, hence enlarged. A virtual image of an object, positioned at the focal plane of a lens, is said to be projected to infinity.
Conventional virtual image displays are known to have many shortcomings. For example, such displays have suffered from being too heavy for comfortable use, as well as too large so as to be obtrusive, distracting, and even disorienting. These defects stem from, among other things, the incorporation of relatively large optics systems within the mounting structures, as well as physical designs which fail to adequately take into account important factors as size, shape, weight, etc.
Recently, holographic optical elements have been used in portable virtual image displays. Holographic optical elements serve as an imaging lens and a combiner where a two-dimensional, quasi-monochromatic display is imaged to infinity and reflected into the eye of an observer. A common problem to all types of holographic optical elements is their relatively high chromatic dispersion. This is a major drawback in applications where the light source is not purely monochromatic. Another drawback of some of these displays is the lack of coherence between the geometry of the image and the geometry of the holographic optical element, which causes aberrations in the image array that decrease the image quality.
New designs, which typically deal with a single holographic optical element, compensate for the geometric and chromatic aberrations by using non-spherical waves rather than simple spherical waves for recording; however, they do not overcome the chromatic dispersion problem. Moreover, with these designs, the overall optical systems are usually very complicated and difficult to manufacture. Furthermore, the eye-motion-box of the optical viewing angles resulting from these designs is usually very small, typically less than 10 mm. Hence, the performance of the optical system is very sensitive, even to small movements of the visor relative to the eye of the viewer.
In some conventional holographic displays a readout light source must be located at some distance from the hologram, in order to illuminate its entire surface. Such configurations lead to holographic display systems which are bulky, space-consuming and sometimes inconvenient to use. International Patent Application No. WO 99/52002, the contents of which are hereby incorporated by reference, discloses compact holographic optical device in which both the aberrations and chromatic dispersions are minimized, and the readout light source must not be located at some distance from the hologram. The disclosed holographic optical device may also act as a beam expander for magnifying a narrow, collimated beam into a beam of larger diameter. Although the overall volume of this compact holographic optical device is substantially reduced compared to other known display devices, the compactness is still insufficient for displays of ultra compact electronic systems such as portable telephones and personal digital assistant.
There is thus a widely recognized need for, and it would be highly advantageous to have, a compact optical device devoid of the above limitation.
According to one aspect of the present invention there is provided an optical device for enlarging an eye box, the optical device comprising: (a) a first optical expander being carried by, or formed in, a first light-transmissive substrate engaging a first plane; and (b) a second optical expander being carried by, or formed in, a second light-transmissive substrate engaging a second plane being spaced apart from the first plane; the first and the second optical expanders being designed and configured such that light passing through the first optical expander is expanded in a first dimension, enters the second light-transmissive substrate, through the second optical expander and exits from the second light-transmissive substrate expanded in a second dimension, hence enlarging an eye box of the optical device in both the first and the second dimensions.
According to another aspect of the present invention there is provided a method of enlarging an eye box, the method comprising: (a) expanding inputted light rays in a first dimension by passing the light rays through a first optical expander engaging a first plane; and (b) expanding the inputted light rays in a second dimension by passing the light rays through a second optical expander engaging a second plane being spaced apart from the first plane; hence enlarging the eye box in both the first and the second dimensions.
According to further features in preferred embodiments of the invention described below, the method further comprising prior to step (b): passing the light rays through an optical trapping element engaging the second plane and being laterally displaced from the second optical expander thereby propagating the light rays through a light guide in a direction of the second optical expander.
According to still further features in the described preferred embodiments the method further comprising collimating the inputted light.
According to still further features in the described preferred embodiments the collimating is done by a converging lens.
According to still further features in the described preferred embodiments the collimating is done by a diffractive optical element.
According to still further features in the described preferred embodiments the method further comprising redirecting the inputted light, so as to reduce a distance between the first plane and an input light source producing the inputted light.
According to still further features in the described preferred embodiments the redirecting is done by a 45 degrees mirror.
According to yet another aspect of the present invention there is provided a method of manufacturing an optical device for enlarging an eye box, the method comprising: (a) positioning a first light-transmissive substrate having a first optical expander carried thereby, or formed therein in a first plane; and (b) positioning a second light-transmissive substrate having a second optical expander carried thereby, or formed therein, the first and the second optical expanders designed and configured such that light passing through the first optical expander is expanded in a first dimension, enters the second light-transmissive substrate, through the second optical expander and exits from the second light-transmissive substrate expanded in a second dimension.
According to still another aspect of the present invention there is provided an optical device for enlarging an eye box, the optical device comprising: a first light-transmissive substrate engaging a first plane; and a second light-transmissive substrate engaging a second plane being spaced apart from the first plane; the first and second light-transmissive substrates designed and configured such that light passing through the device is first expanded in a first dimension within the first light-transmissive substrate, and then expanded in a second dimension within the second light-transmissive substrate, hence enlarging an eye box of the optical device in both the first and the second dimensions.
According to further features in preferred embodiments of the invention described below, the optical device further comprising an input light source for producing the light.
According to still further features in the described preferred embodiments the optical device further comprising: (c) an optical trapping element being carried by, or formed in, the second light-transmissive substrate and being laterally displaced from the second optical expander;
According to still further features in the described preferred embodiments the optical device further comprising a collimator for collimating the light produced by the input light source.
According to still further features in the described preferred embodiments the optical device further comprising at least one optical element for redirecting light rays, positioned so as to reduce an overall size of the optical device.
According to still further features in the described preferred embodiments the first and second planes are substantially parallel.
According to still further features in the described preferred embodiments the first and second dimensions are substantially orthogonal.
According to still further features in the described preferred embodiments the input light source comprises an input display source, hence the light constitutes an image.
According to still further features in the described preferred embodiments the first and second optical expanders substantially parallel one another and at least partially overlap in a direction substantially perpendicular both thereto.
According to still further features in the described preferred embodiments the first optical expander is configured and designed so as to transform spherical waves emanating from the input display source into plane waves, to at least partially diffract the plane waves, and to reflect the plane waves within the first light-transmissive substrate, hence to expand the image in the first dimension.
According to still further features in the described preferred embodiments the second optical expander is configured and designed so as to at least partially diffract at least a portion of light rays exiting the first light-transmissive substrate, hence to expand the image in the second dimension, and to couple the light rays out of the second light-transmissive substrate in a direction of an eye of a user.
According to still further features in the described preferred embodiments the optical trapping element is configured and designed so as to trap at least a portion of light rays exiting the first light-transmissive substrate, inside the second light-transmissive substrate by substantially total internal reflection, hence to propagate the plurality of light rays in a direction of the second optical expander.
According to still further features in the described preferred embodiments the second optical expander is configured and designed so as to at least partially diffract the plurality of light rays, propagated through the second light-transmissive substrate, hence to expand the image in the second dimension, and to couple the plurality of light rays out of the second light-transmissive substrate in a direction of an eye of a user.
According to still further features in the described preferred embodiments each of the first and the second optical expanders is embodied in the light-transmissive substrates by recording an interference pattern of two mutually coherent optical waves.
According to still further features in the described preferred embodiments the interference pattern comprise linear diffraction gratings.
According to still further features in the described preferred embodiments the linear diffraction gratings of the second optical expander is substantially orthogonal to the linear diffraction gratings of the first optical expander.
According to still further features in the described preferred embodiments the linear diffraction gratings of the first and second optical expanders are each independently selected from the group consisting of reflection linear diffraction gratings and transmission linear diffraction gratings.
According to still further features in the described preferred embodiments the recording is effected by a procedure selected from a group consisting of computer-generated masks, lithography, embossing, etching and direct writing.
According to still further features in the described preferred embodiments the optical trapping element is embodied in the light-transmissive substrates by recording an interference pattern of two mutually coherent optical waves.
According to still further features in the described preferred embodiments the linear diffraction gratings of the optical trapping element is substantially orthogonal to the linear diffraction gratings of the first optical expander.
According to still further features in the described preferred embodiments the linear diffraction gratings of the optical trapping element is substantially parallel to the linear diffraction gratings of the second optical expander.
According to still further features in the described preferred embodiments the linear diffraction gratings of the second optical expander and the optical trapping element are with equal periodicity.
According to still further features in the described preferred embodiments each of the first and second light-transmissive substrates comprises a first surface and a second surface.
According to still further features in the described preferred embodiments the first optical expander is embodied in the first surface of the first light-transmissive substrate.
According to still further features in the described preferred embodiments the first optical expander is embodied in the second surface of the first light-transmissive substrate.
According to still further features in the described preferred embodiments the collimator comprises a converging lens.
According to still further features in the described preferred embodiments the collimator comprises a diffractive optical element carried by or formed in, the first light-transmissive substrate.
According to still further features in the described preferred embodiments the at least one optical element is a 45 degrees mirror.
According to still further features in the described preferred embodiments each of the first optical expander and the second optical expander has a predetermined diffraction efficiency.
According to still further features in the described preferred embodiments the optical trapping element has a predetermined diffraction efficiency.
According to still further features in the described preferred embodiments the predetermined diffraction efficiency varies locally for achieving an output having substantially uniform light intensities.
According to still further features in the described preferred embodiments the predetermined diffraction efficiency varies locally for achieving an output having predefined intensities.
According to still further features in the described preferred embodiments the first and the second optical expanders are each independently a plurality of linearly stretched mini-prisms, carried by a variable light transmissive surface.
According to still further features in the described preferred embodiments the optical trapping element is a plurality of linearly stretched mini-prisms.
According to still further features in the described preferred embodiments the first light-transmissive substrate and the second light-transmissive substrate are of thickness ranging between about 0.5 mm and about 5 mm.
According to still further features in the described preferred embodiments the first light-transmissive substrate and the second light-transmissive substrate are each independently selected from the group consisting of glass and transparent plastic.
The present invention successfully addresses the shortcomings of the presently known configurations by providing an optical device for enlarging an eye box.
Implementation of the method and device of the present invention involves performing or completing selected tasks or steps manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of preferred embodiments of the method and device of the present invention, several selected steps could be implemented by hardware or by software on any operating device of any firmware or a combination thereof. For example, as hardware, selected steps of the invention could be implemented as a chip or a circuit. As software, selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating device. In any case, selected steps of the method and device of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.